In recent years, flat panel displays have been utilized in various products and fields, and there are demands for flat panel displays having even larger sizes, even higher picture quality, and even lower power consumption.
In view of such circumstances, organic electroluminescent (referred to as EL below) display devices provided with organic EL elements utilizing the electroluminescence of organic materials are attracting much attention as flat panel displays due to their excellent qualities, such as low voltage driving, high responsiveness, and self-luminosity, while being in a completely solid state.
An organic EL display device has a configuration including, for example, thin film transistors (TFTs) provided on a substrate, such as a glass substrate, and organic EL elements provided on the substrate connected to the TFTs.
Organic EL elements are light emitting elements capable of emitting light at high luminance using low voltage direct current driving, and have a configuration in which a first electrode, an organic EL layer, and a second electrode are layered in this order.
An organic EL layer is an organic compound layer including a light emitting layer. A full color organic EL display device generally includes organic EL elements of each color for red (R), green (G), and blue (B) formed in an array on the substrate as sub pixels. TFTs are employed in a full color organic EL display device to display pictures by selectively causing these organic EL elements to emit light at a desired luminance.
However, generally, a portion of light from the light generated in the light emitting layer of each of the organic EL elements is not externally extracted from the organic EL element, but instead, propagates inside the organic EL element and is trapped within the organic EL element due to reflection, such as at the interfaces between the first electrode or the second electrode and the organic EL layer.
Thus, regarding organic EL display devices, there is a proposal for a method of externally extracting the portion of the light trapped within the organic EL elements. In the proposed method, light which is being reflected at interfaces, propagating within the organic EL elements, and not externally extractable from the organic EL elements (being attenuated due to a light propagation distance limit) is reflected using a plurality of walls and sloping banks having reflecting properties (see, for example, PTL 1).
FIG. 13A is a plan view illustrating a schematic configuration of sub pixels 510R, 510G, and 510B in an organic EL display device 500 described in PTL 1. FIG. 13B is a cross-sectional view taken along line J-J of the sub pixel 510R illustrated in FIG. 13A.
As illustrated in FIG. 13A, the organic EL display device 500 has a configuration in which a plurality of sub pixels 510R, 510G, and 510B configured to exhibit each of three different colors, red (R), green (G), and blue (B), are each arranged within a display region.
As illustrated in FIG. 13B, the sub pixels 510R are each divided into a plurality of light emitting regions 510Ra by partitions 527 serving as non-light-emitting regions (see FIG. 13B). Similarly, the sub pixels 5100 and 510B are each divided into a plurality of light emitting regions 510Ga and 510Ba.
As illustrated in FIG. 13B, the organic EL display device 500 includes a substrate 520 on which TFT circuit portions 521 are formed, and side layers 523 disposed on the substrate 520, with a flattened layer 522 interposed between the substrate 520 and the side layers 523. A first electrode 525 is disposed on the flattened layer 522 and the side layers 523. Reflection structures 526 are formed by the side layers 523 and the first electrode 525.
As illustrated in FIG. 13A, first electrodes 525 are isolated from each other for each of the sub pixels 510R, 510G, and 510B. The first electrode 525 for each of the sub pixels 510R, 510G, and 510B is electrically connected to a different respective TFT circuit portion 521 (TFT drive circuit) through a contact portion 524. A plurality of light emitting regions within the same sub pixel, for example, the plurality of light emitting regions 510Ra within the sub pixel 510R, have a common first electrode 525, and so are driven by the same TFT circuit portion 521.
As illustrated in FIG. 13B, the partitions 527 are disposed on the first electrode 525, and cover the first electrode 525 on the side layers 523 and the first electrode 525 at the contact portion 524.
An organic EL layer 528 including at least a light emitting layer is disposed above the first electrode 525. A second electrode 529 is disposed on the organic EL layer 528 spanning across an entire display region 501. Organic EL elements are configured by the first electrode 525, the organic EL layer 528, and the second electrode 529. Since the partitions 527 are disposed on the first electrode 525, the organic EL layer 528 above the reflection structures 526 does not emit light. Regions within trenches 530 (indentations) formed by the partitions 527 and lying between the partitions 527 are employed as the light emitting regions 510Ra, 510Ga, and 510Ba.
According to PTL 1, the reflection structures 526 include inclined faces at the side layers 523, and, out of the light emitted by the light emitting regions, light travelling in the in-plane direction of the substrate 520 is reflected by the first electrode 525 on the inclined faces.
Thus, according to PTL 1, a portion of light trapped within the organic EL elements is reflected by the reflection structures 526 at the trenches 530, enabling external extraction from the organic EL elements, and enabling the light extraction efficiency to be increased.